It is the purpose of this proposed research to investigate and quantitatively characterize the myogenic vasomotor response to alterations in transmural pressure in the precapillary resistance vessels in the wing web of the bat. The specific aim of the research is to quantitatively investigate the dynamics and rate sensitivity of the vasomotor response to step and ramp forms of transmural pressure stimuli. The time course of the changes in microvessel diameter and wall force in response to an alteration in transmural pressure will be analyzed in an attempt to determine the dynamic, mechanical characteristics of this nyogenic response. In addition, the following related experiments are proposed: (1) to study the influence of the initial vessel diameter and wall tension on the subsequent myogenic response to a transmural pressure stimulus, (2) to perform longitudinal studies o the myogenic reactivity of the same vessels to study the reproducibility and variability of a single vessel's responsiveness over a short period of time, (3) to describe some of the ultrastructural changes which occur in the smooth muscle and endothelium of these microvessels at various levels of transmural pressure and, thus, myogenic tone, (4) to evaluate the role played by neural factors in the modulation of the pressure-induced myogenic response observed in these vessels, and, (5) to examine the effects of pharmacological interventions aimed at modifying transsarcolemmal calcium current in the smooth muscle on the myogenic reactivity of the microvessels. The experimental model to be employed in the proposed research is the microcirculation in the wing web of the intact, unanesthetized bat. A considerable amount of data has accumulated which points dirctly and indirectly to the existence of an intrinsic pressure-sensitive mechanism in the microcircularory resistance vessels which is thought to contribute in an important way to many different kinds of peripheral circulatory phenomena. It is the goal of the proposed project to directly and quantitatively characterize the vasoactive responsiveness of the relevant microcircularory resistance vessels to various forms of transmural pressure stimuli and, further, to examine some possible cellular mechanisms which may be responsible for transducing the change in transmural pressure to an active vascular response.